Leaf water potential of coffee estimated by landsat-8 images.

Traditionally, water conditions of coffee areas are monitored by measuring the leaf water potential (ΨW) throughout a pressure pump. However, there is a demand for the development of technologies that can estimate large areas or regions. In this context, the objective of this study was to estimate the ΨW by surface reflectance values and vegetation indices obtained from the Landsat-8/OLI sensor in Minas Gerais-Brazil Several algorithms using OLI bands and vegetation indexes were evaluated and from the correlation analysis, a quadratic algorithm that uses the Normalized Difference Vegetation Index (NDVI) performed better, with a correlation coefficient (R2) of 0.82. Leave-One-Out Cross-Validation (LOOCV) was performed to validate the models and the best results were for NDVI quadratic algorithm, presenting a Mean Absolute Percentage Error (MAPE) of 27.09% and an R2 of 0.85. Subsequently, the NDVI quadratic algorithm was applied to Landsat-8 images, aiming to spatialize the ΨW estimated in a representative area of regional coffee planting between September 2014 to July 2015. From the proposed algorithm, it was possible to estimate ΨW from Landsat-8/OLI imagery, contributing to drought monitoring in the coffee area leading to cost reduction to the producers.

Salt stress and exogenous silicon influence physiological and anatomical features of in vitro-grown cape gooseberry / Estresse salino e silício exógeno influenciam características fisiológicas e anatômicas de fisális cultivada in vitro

ABSTRACT: Salt stress is one of several major abiotic stresses that affect plant growth and development, and there are many evidences that silicon can ameliorate the injuries caused by high salinity. This study presents the results of an assay concerning: (1) the effect of in vitro NaCl-induced salt stress in cape gooseberry plants and (2) the possible mitigating effect of silicon in saline conditions. For that, nodal segments were inoculated in Murashige and Skoog (MS) medium under salinity (0.5 and 1.0% NaCl) with different silicic acid concentrations (0, 0.5 and 1.0g L-1). Phytotechnical characteristics, photosynthetic pigments content, and leaf anatomy were evaluated after 30 days. Shoot length, root length, number of leaves and buds, fresh and dry weight, pigment content, stomatal density and leaf blade thickness were drastically reduced by increased salt level. The supply of silicon (1.0g L-1) has successfully mitigated the effect of salinity at 0.5% NaCl for chlorophyll, carotenoids, stomatal density and leaf blade thickness. When salt stress was about 1.0%, Si was not effective anymore. In conclusion, we affirmed that, in in vitro conditions, salt stress is harmful for cape gooseberry plants and the addition of silicon showed effective in mitigating the saline effects of some features.

RESUMO: O estresse salino é um dos tipos de estresses abióticos mais severos que afetam o crescimento e desenvolvimento vegetal e existem muitas evidências de que o silício possa amenizar os danos causados pela elevada salinidade. Este estudo apresenta os resultados de uma pesquisa que investigou: (1) o efeito do estresse salino in vitro induzido por NaCl em plantas de fisális e (2) o possível efeito mitigador do silício nas condições salinas. Para isso, segmentos nodais foram inoculados em meio de cultura Murashige e Skoog com dois níveis de salinidade (0,5 e 1,0% de NaCl) adicionado de ácido silícico (0; 0,5 e 1,0g L-1). Características fitotécnicas, conteúdo de pigmentos fotossintéticos e anatomia foliar foram avaliados aos 30 dias. O comprimento da parte aérea e da raiz, número de folhas e gemas, massa fresca e seca, conteúdo de pigmentos, densidade estomática e espessura do limbo foliar diminuíram drasticamente devido ao aumento do nível de salinidade. A aplicação de 1,0g L-1 silício atenuou com sucesso os efeitos salinos para as variáveis conteúdo de pigmentos e anatomia foliar quando a salinidade era de 0,5% NaCl. Já quando o nível de NaCl dobrou, o silício não se mostrou efetivo. Concluindo, pode-se afirmar que, em condições in vitro, o estresse salino é prejudicial à fisális e a adição de silício mostra-se efetiva na mitigação dos efeitos salinos em determinadas características.